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Bendis, Randall (2015) WETLAND DEFENSE: INSECTICIDE RESISTANCE IN NON-TARGET ORGANISMS AND ITS COMMUNITY-WIDE IMPLICATIONS. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Anthropogenic stressors are ubiquitous and have been implicated in species declines worldwide. Pesticides are one such stressor that can have profound effects on aquatic communities by directly affecting sensitive species and indirectly affecting other species via trophic cascades, which can alter ecosystem function. However, there is growing evidence that non-target species can evolve increased resistance to these chemicals. When such species are important drivers of the food web, such as zooplankton, then evolved resistance should help buffer communities from the effects of pesticides. Furthermore, given that some species can evolve cross-resistance to other pesticides, one would predict that cross-resistance could have pronounced effects on community stability.
The studies herein attempt to address these concerns through a series of experiments that build on each other in complexity. In the first study, we found that populations of two common, co-occurring zooplankton species collected from ponds near surrounding agriculture were more resistant to a commonly applied insecticide (chlorpyrifos) and this variation was correlated with surrounding agricultural land use. In the second study, we utilized this pre-existing variation in resistance to determine whether resistant populations of zooplankton could buffer an entire aquatic community from the effects of pesticides. Chlorpyrifos caused direct mortality of zooplankton in communities containing sensitive populations and this led to a bloom of phytoplankton and subsequent declines in periphyton abundance and amphibian mass and survivorship. In the third study, we exposed communities to several concentrations of AChE-inhibiting or sodium channel-inhibiting insecticides. We discovered that communities containing resistant zooplankton were buffered from adverse effects at low-to-moderate concentrations of all AChE-inhibiting insecticides, but were not buffered against sodium channel-inhibiting insecticides. Conversely, communities with sensitive zooplankton experienced pronounced trophic cascades when exposed to all insecticides. The fourth study manipulated the diversity of zooplankton within the experimental communities. We discovered that populations of cladocerans and copepods living near agriculture were more resistant to chlorpyrifos, but rotifers did not show a clear pattern of variation in that could be associated with land use. Furthermore, unlike communities with cladocerans, communities containing only copepods and rotifers were unable to buffer the community from the effects of the pesticide.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Bendis, Randallrjb26@pitt.eduRJB26
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairRelyea,
Committee MemberMorehouse, Nathannim@pitt.eduNIM
Committee MemberKalisz, Susankalisz@pitt.eduKALISZ
Committee MemberRebeiz, Markrebeiz@pitt.eduREBEIZ
Committee MemberWeider,
Date: 17 June 2015
Date Type: Publication
Defense Date: 2 April 2015
Approval Date: 17 June 2015
Submission Date: 16 April 2015
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 241
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: ecology, evolution, insecticide resistance, toxicity, zooplankton, Daphnia, aquatic community, trophic cascade, wetlands, ecotoxicology, community ecology
Date Deposited: 17 Jun 2015 13:39
Last Modified: 15 Nov 2016 14:27


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